The present invention relates generally to high frequency millimeter wave integrated circuit amplifiers, and more particularly relates to such high frequency amplifiers configured for use at frequencies of 75 GHz and higher.
The design and manufacture of high frequency, millimeter wave integrated circuit devices presents many challenges not found in the construction of other types of integrated circuits. However, the design and manufacture of circuits for operation in the W-band and above, frequencies of approximately 75 GHz and above, present particular challenges, as circuits and structures suitable for use even at lower millimeter wave frequencies, for example as may be suitable for devices operating at 30 GHz, do not function similarly or adequately at 75 GHz and above.
As will be apparent to those skilled in the art, structures such as filters suitable for use at the identified higher frequencies must be adapted for such frequencies. Additionally, however, the placement and configuration of signal and voltage lines can present substantial problems of resonance or “ringing” of the circuits. These problems are heightened when the integrated circuit is an amplifier, particularly one offering relatively high gain and power; and particularly when there is a need to form the amplifier in a minimal area on a substrate, for example a minimally-sized semiconductor die. Forming such an amplifier on a minimally-sized die is highly advantageous from a cost perspective, as smaller die will yield more die per semiconductor wafer, thus providing more devices for essentially no increase in the cost of wafer processing. Additionally and importantly, from an application perspective, the smaller a die may be made, the less space it takes in a final system; and such smaller size is often a significant factor in the system design.
Conventionally, relatively high power, multi-stage, millimeter wave amplifier circuits rely upon design rules resulting in relatively large spaces between signal lines and other components in order to avoid the above-described resonance or ringing. While these design rules are generally effective for such purposes, the resulting large spaces increase the total area occupied on a die by such an amplifier. Additionally, with such conventional design methodologies, a power buss for gate bias voltage is typically routed along the periphery of the die to minimize distortion of the voltage signals from the high-frequency signals being amplified. Such a structure, and the routing of voltage lines from the peripheral busses to individual amplifier stages, with the lines surrounded by substantial open area to reduce the risk of interference that result from such a structure, again require additional space on a die, and thereby again increase the relative size of the die. Additionally, for drain bias, discrete bias pads are typically provided for each amplifier stage, again occupying substantial area on the die. Accordingly, for such high frequency millimeter wave amplifiers, the conventional design criteria and methodology tend to increase the size of the device where compactness would be an asset.
Accordingly, the present invention provides a new configuration for and method of construction of a multi-stage, millimeter wave amplifier integrated circuit, where the circuit is intended for operation at 75 GHz and above, and where the amplifier may be constructed with relatively high gain and power output, as will be described later herein, and where the amplifier may also be constructed more compactly than has been feasible for conventional devices of such type.